Diagnosis of knee prosthetic joint infection; aspiration and biopsy

Authors/contributors
Abstract
Background: Prosthetic joint infection (PJI) is a significant cause of morbidity and mortality following knee replacement surgery. The diagnosis can be challenging and is based on a combination of clinical suspicion, radiographic findings and also biochemical/ microbiological investigations. Our Aim was to review the role of aspiration and biopsy in the diagnosis of PJI in Total Knee Arthroplasty (TKA). Method/results: Aspirated synovial fluid should be analysed by direct culture, via blood culture bottles, EDTA bottles for cell count and ‘point of care’ testing such as leucocyte esterase or alpha defensin. Synovial WCC and PMN cell percentage are important steps in diagnosis of both acute and chronic PJI. A minimum of 5 deep samples using a 5 clean instrument technique should be obtained and sent for tissue culture done either blind or arthroscopic. Formal fluoroscopic guided interface biopsy has also been described with excellent results. In a recent series of 86 TKRs preoperative arthroscopic biopsy group had a sensitivity of 100%, specificity of 94.7%, positive predictive value of 87.4% and a negative predictive value of 100%. Conclusion: In the presence of clinical suspicion with raised biomarkers, it is recommended that aspiration +/- biopsy with synovial fluid testing is performed. Direct culture and cell count are recommended. ‘Point of care tests’ such as Leucocyte Esterase testing should be considered. Duration of culture, including pathogen and host factors, should be discussed with a local microbiology/ID department in the context of a formal multidisciplinary team.
Publication
The Knee
Date
06/2021
Notes

Summary:

Prosthetic joint infection (PJI) is a significant complication following knee replacement surgery, with an incidence ranging from 1% to 12%. Diagnosis of PJI can be challenging and relies on a combination of clinical suspicion, radiographic findings, and biochemical/microbiological investigations.

Pre-operative joint aspiration is the mainstay microbiological tool for diagnosing PJI. It has shown a pooled sensitivity of 0.78 and specificity of 0.96 in total knee arthroplasty patients. Blood tests, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are essential in diagnosing PJI, along with radiological assessment using X-rays. The synovial fluid obtained through aspiration should be sent for analysis, including culture, cell count, and point-of-care testing.

Identification of the causative microorganism is crucial for targeted antibiotic treatment and long-term eradication of PJI. Joint biopsy, obtained through blind or formal arthroscopic techniques, is necessary to obtain tissue samples for culture and histological assessment. During biopsy, 5 independent samples using separate sterilized instruments is currently recommended. The biopsy samples should be incubated for at least 7 days, with a longer incubation period for atypical organisms. Consider repeat aspiration and/or biopsy if negative first culture but suspicion remains high. Antibiotics should be stopped for a minimum of 2 weeks prior to pre-operative sampling.

Pre-operative joint biopsy has a reported sensitivity of 100% and specificity of 94.7% in diagnosing PJI, while alternative techniques like interface biopsy have shown a sensitivity of 88.2% and specificity of 100%. These techniques can be used when aspiration fails to identify the causative organism or when there is significant doubt. Duration of culture, including pathogen and host factors, should be discussed with a local microbiology/ID department

Citation
1.
Salar O, Phillips J, Porter R. Diagnosis of knee prosthetic joint infection; aspiration and biopsy. The Knee. 2021;30:249-253.